Definition 2 (Robust control invariant set [1]}) 
A set \(\mathbb {X}_r \subseteq \mathbb {X}\)  is said to be a robust control invariant set (RCIS) for system (REF ) if for every \(x(n) \in \mathbb {X}_r\) , there exists a feedback control law \(u(n) = \mu (x(n)) \in \mathbb {U}\)  such that \(\mathbb {X}_r\)  is forward invariant for all \(w(n) \in \mathbb {W}\) .

